Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system (CNS) characterized by mononuclear cell infiltration with subsequent demyelination of axonal tracts leading to progressive paralysis. The precise immunologic mechanisms involved in the induction and chronic course of MS are poorly understood, and there are limited therapeutic options for managing this disease. The goal of this proposal is to characterize a potential cell based therapy in modulating pathogenic and regulatory T cell responses. Adult human stem/progenitor cells from bone marrow (hMSCs) produce improvements in models of neurodegeneration in part through immunomodulatory effects. In experimental autoimmune encephalomyelitis (EAE), an autoreactive T cell-mediated mouse model of MS, systemic administration of hMSCs alleviates clinical symptoms. This proposal seeks to determine how hMSCs modulate the systemic immune response in EAE to promote functional recovery. We hypothesize that hMSCs modulate differentiation and activation of specific T cell subsets to alter the systemic immune profile in a model of demyelination. The first objective will characterize the T cell population in hMSC-treated EAE mice. Cellular immune responses will be assessed in vivo, and T cells isolated from peripheral immune organs and CNS at specific time points will be cultured ex vivo. T cells will be stimulated with the immunizing peptide; proliferation and activation will be assessed by proliferation and cytokine production assays. T cell phenotype will be assayed by flow cytometric analysis. Functional effects on myelination will be assayed using a newly developed flow cytometric assay to enumerate cells of the oligodendrocyte lineage in the brain and lumbar spinal cord and validated by immunohistochemical assays. We expect hMSCs administered at EAE onset to functionally suppress pathogenic T cells and to promote myelin repair. The second objective will investigate hMSC-mediated immunomodulatory effects on T cell subsets in vitro. T cells isolated from mice will be cultured under neutral or lineage-driving culture conditions (Th1, Th17, Th2, Treg). T cell subsets will be stimulated in the absence or presence of hMSCs in direct co-culture or indirect co-culture using a transwell culture system. Alternatively T cells will be stimulated in the presence of hMSC conditioned medium. T cell proliferation, suppression, phenotype, and cytokine production will be assayed. We expect hMSCs mediate pleiotropic immunomodulatory effects on T cells in part by secretion of soluble molecules. PUBLIC HEALTH RELEVANCE: Multiple Sclerosis (MS) is an immune-mediated disease of the central nervous system characterized by inflammation and loss of myelin that supports neuronal conduction. Despite years of extensive research there is a distinct lack of highly effective treatments for the management of MS as the search for a cure remains ongoing. This proposal will characterize a potential cell-based therapy using human stem/progenitor cells from bone marrow to modulate immune responses so as to prevent damage and promote repair in an animal model of MS.